1. Field of the Invention
The present invention relates generally to an optical flow imaging and analysis configuration used in particle analysis instrumentation, and more particularly to a high numerical aperture optical flow imaging system incorporating a flow chamber, immersion oil and high numerical aperture optics, including a high numerical aperture oil-immersion objective.
2. Description of the Prior Art
The art has seen various optical/flow systems employed for transporting a fluid within an analytical instrument to an imaging and optical analysis area. A liquid sample is typically delivered into the bore of a flow chamber and this sample is interrogated in some way so as to generate analytical information concerning the nature or properties of the sample. For example, a laser beam may excite the sample that is present in the bore of the capillary, with the emitted fluorescence energy representing the signal information.
From an optical perspective, the objectives and flow chambers in the prior art have been of medium numerical aperture (NA). A typical flow cytometer comprises a cylindrical or rectangular glass rod having a hollow co-axial cylindrical or rectangular bore of smaller diameter, in which the sample to be analyzed is placed. With the sample in place, optical analysis is performed with low to medium numerical aperture (NA) optics (e.g., NA=0.6), typically an air objective. Such low to medium NA optics only are employed in present flow cytometry systems because they are considered easier to use and more suitable for dealing with the limitation of having the fluid of interest spaced from the optics by the thickness of the rod wall, which are simply too thick to permit use of high NA optics.
The inefficiencies of optically imaging with air microscope objectives into and out of the flow cell may include a mediocre resolution, less-than-optimum collection of the image illumination energy from the sample, less than optimum illumination of the sample with fluorescence excitation light and less than optimum collection of fluorescence emissions from the sample.
To date, therefore, the imaging flow cytometer art has not disclosed utilizing oil-immersion objectives to deliberately optimize the imaging resolution and fluorescence excitation and fluorescence emission collection. There is therefore a need in the art for a simple and economical mechanism to increase the resolution and fluorescence efficiency.